Optically tracked projectile

ABSTRACT

A projectile, that can be tracked optically, which is coated with a fluorescent die or affixed with rearward facing retro-reflectors. Laser emitted radiation forms a cone of light that intersects and illuminates the ballistic path of the projectile. It is possible to manual measurement techniques, spotters or automated tracking of the illuminated projectile. The optically tracked projectile allows for the adjustment subsequent shots using a manual or automated optical tracking.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from the U.S. Provisional ApplicationNo. 61/803,826 filed Mar. 21, 2013; U.S. patent application Ser. No.14/220,404 filed Mar. 20, 2014; and U.S. Provisional Application No.62/201,255 filed Aug. 5, 2015. The subject matter of said patentapplication Ser. No. 14/220,404 is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to an ammunition projectile that allowsfor position observation when illuminated. The projectile my functionwith a fire control device that tracks the path of a projectile while inballistic flight toward a given target, so as to improve precision andaccuracy when aiming a subsequent projectile at the same or anothertarget.

Tracer technology was developed by the British defense researchestablishment in the midst of the 1^(st) World War. The technologycontinues to be used 100 years later. In machine guns, belts ofammunition are mixed—ball and tracer combinations. Unfortunately the 100year-old technology has a number of practical drawbacks: (1) The tracerammunition's ballistics differs from the trajectory of ball ammunition,(2) handling and inclusion of pyrotechnic tracers in ammunitionsignificantly increases the cost of ammunition, (3) tracers causeunwanted range fires in training, (4) the glow emitted by tracers'backlights friendly forces, vehicles, equipment and aircraft and (5)tracers are not optimized for automatic tracking technology.

Simple Deployment and Use:

The invention disclosed in this application provides for a projectileaffixed with retro-reflectors that reflect light from an optical strobeemitter. Where the reflected light is in the visual spectrum, a sniperspotter can observe the projectile's path and make adjustments forsubsequent shots as the methodology allows a trained spotter to detectthe influence of wind on the projectile and to calculate an effectiveadjustment for the sniper. This technique is also useful where theprojectile is illuminated in the near infra-red (NIR) and the reflectedbeam is viewed with NIR night vision goggles.

Use and Deployment on Aircraft:

It is useful to discuss this methodology if deployed in an air-to-groundapplications where the wind wash from helicopter rotors, speed of theaircraft, etc., make it very difficult to correctly place fires fromdoor guns. Current tracer technology emits light during the entireflight path allowing enemy on the ground to quickly locate friendlyhelicopters. With the approach disclosed in this application, a doorgunner with night vision goggle will emit short pulses of NIR laseremissions and the retro-reflectors on the ammunition will allow thegunner to track the path of ammunition. This is done without thebacklighting of the helicopter which is created by tracers. The narrowbeam of pulsed NIR illumination is almost undetectable and the low powerrequired of emitters coupled with retro-reflectors reduces the signatureof the gunner—especially compared to the current technique of firingvisible tracer ammunition. The NIR light reflected from a projectileallows the gunner to track the trajectory of ammunition withoutaffording the enemy with a means of detecting the helicopter.

Retro-Reflection:

Use of retro-reflectors is ubiquitous in road signs where the technologywas invented in the United Kingdom and introduced in the late 1930s.Retro-reflectors reflect light to the emission source with a minimum ofscattering. There are three principle types of retro-reflectors: cornercube reflectors, cat eyes and phase conjugated mirrors. The coefficientof luminosity returned in the direction of the emission source is high.In addition to their use on road signs, retro-reflectors are used insafety reflectors, high visibility clothing and surveying. NASA has alsoused this technology. The Apollo 11, 14 and 15 missions placedretro-reflectors on the moon surface allowing for precise measurementsof the moon.

Automated Tracking, Shot Registration:

In addition to providing improved techniques to visually track thetrajectory of ammunition in flight, one can also add an optical, imageror laser tracker (detector) coupled to a fire control system to furtherautomate the system. In some cases it is useful to pulse the laser lightemission to simplify the automated optical detection. Each method ofautomated tracking allows for “registration” of the shot at specific waypoints along the trajectory, when coupled to a fire control computerutilizing a regressive ballistic algorithm. Alternatively, the detectorcan use a MEMS steered laser tracking system where the optical detectorsteers the laser to maintain illumination of a retro-reflector affixedto the ammunition. In this case, the MEMS steered device measures the Xand Y changes of the projectile during the entire flight path. Opticaldetection of MEMS steered laser emitters allow for automation so thatreal time “registered” data is collected.

Regressive Ballistic Algorithm and Improved Shot Placement:

An automated system can utilize acquired real time “registered” datawith a regressive algorithm. A regressive algorithms use statisticalprocesses to estimate relationships among variables and with a pattern.The algorithm improves the fidelity of predictive fire control tocorrect for unmeasured aiming errors due to wind turbulence,altitude-dependent wind conditions, lot-to-lot ammunitionirregularities, bore sight misalignment and the like, for use whenfiring subsequent projectiles. Using this methodology, the merging ofregistered actual shot data with fire control algorithms provides forimproved solution fidelity with better placement of the subsequent shot.

Prior Art

The U.S. Pat. No. 8,074,555, and its predecessor Provisional ApplicationNo. 61/803,826, disclose a system for tracking the lateral drift andvertical drop of an ammunition projectile while in flight to provide aprecise aim point for firing one or more subsequent projectiles. Withthis system, a projectile is illuminated by an optical emitter housed inthe projectile. The system produces an optical strobe signals atpredetermined times (T1, T2, T3 . . . ) following firing of theprojectile (at time T0). An optical detector receives the opticalsignals and an image processor determines the lateral drift (i.e. X1,X2, X3 . . . ) and vertical drop (i.e. Y1, Y2, Y3 . . . of theprojectile at the predetermined times (T1, T2, T3 . . . ) following timeT0. The subject matter of this patent is incorporated herein byreference.

This prior art uses the real time data to correct for aiming errors dueto gun jump, wind turbulence, altitude-dependent wind conditions,lot-to-lot ammunition irregularities, bore sight misalignment and thelike, for use when firing subsequent projectiles. This system isoptimized to function with projectiles that have adequate energy topower LED's to emit strobe light and where the ballistic trajectoryangles are significant (e.g., with mortars, artillery and 40 mmsystems).

SUMMARY OF THE INVENTION

The principal object of the present invention is to provide for anobservable and trackable projectile that, when coupled to a emitterallows for the observation and recording of a projectile in flight.Further, when coupled to a fire control system, the recording of actualflight drop, drift and measurement of a projectile in flight allows forimproved precision and accuracy of weapon systems.

It is a further object of the invention to provide a method that avoidsthe drawbacks of firing conventional tracer ammunition.

It is another object of the present invention to improve the firecontrol device of the type disclosed in the U.S. Pat. No. 8,074,555 torender it more reliable and less expensive.

It is still another object of this invention to improve the fire controldevice disclosed in the U.S. Pat. No. 8,074,555 to minimize powerconsumption of projectile-borne batteries, used for example inprojectile fuses, and to simplify the sensor array (detector) that viewsthe projectile.

These objects, as well as still further objects which will becomeapparent from the discussion that follows, are achieved, in accordanceto the present invention by providing an otherwise conventionalammunition projectile with methods and apparatus that use a pulsingelectro-optical emitter and an optical tracking device to locate aradiated projectile in flight.

In one preferred embodiment of the invention, retro-reflectors areaffixed, coated or otherwise fitted to a projectile's rear surfaceprovide for reflection of light that can be viewed by electro-opticaldevices in the vicinity of the weapon firing said projectile. Theradiated light emission from the laser emitter may be in the UV, visual,NIR or MWIR spectrum. The light reflected from the retro-reflectivematerial may be in the UV, visual, NIR or MWIR spectrum.

The provision of projectiles with retro-reflectors according to theinvention allows for use of a range of emission devices and is usefulwithout specialized detectors so the fielding of the technology isstraightforward. Accordingly, the system will function in the currentspectrum of night vision equipment and can be readily integrated intoexisting sniper's kit when fitted with a laser emitter that reflectsfrom retro-reflectors on a projectile.

With respect to retro-reflection and recent prior art for tracers, U.S.Pat. No. 5,267,014 provided a methodology for non-contact measurement toobtain 6DOF measurement in objects by means of a retro-reflector.Earlier work in this field developed the principles of 3DOF measurementof objects by means of retro-reflectors. U.S. Pat. No. 6,097,491identified a method to use beam splitting for measurement. Using theprior work, Ruag GmbH in Germany has developed a family of trainingdevices incorporating retro-reflectors on targets as disclosed in U.S.Pat. No. 6,139,323, allowing for realistic military training. 3M holds anumber of patents for retro-reflective device manufacture and designthat are instructive and several patents that disclose methods to limitthe retro-reflector's performance spectrum, for example as in U.S. Pat.No. 8,567,964. U.S. Pat. No. 6,808,467 describes a covert tracerprojectile to determine aiming error using an optical collimator tosteer a projectile to an illuminated target. U.S. Pat. No. 8,402,892describes a method of producing covert tracers. U.S. Pat. No. 8,168,804identifies types of dyes that can provide a NIR response with a Stoke'sshift response.

Configuration:

The selection and orientation of the retro-reflectors affixed or coatedon the projectile provides geometric line of site from the projectile'sbase or projectile body such that light is reflected rearward, towardthe origin of the projectile's flight. The retro-reflective material ispositioned and oriented on the projectile to allow for the rearwardtravel of light, notwithstanding that a flying projectile is subject toa yawing motion and angular flight characteristics associated with aparticular projectile. The present invention provides that either aspotter or automated tracking system corrects the aim of a weaponadjusting or updating the ballistic firing solution.

Cone of Illumination:

Preferably the radiation source is laser source adapted to be affixed tothe weapon so that the cone of illumination of the laser sourceintersects with the ballistic path of the projectile. The cone of laserlight dispersion should encompass the ballistic path of the flight andalso allow for post shot movement of the laser affixed to the weapon.

Spectrum:

Depending upon the type of laser and retro-reflectors, the illuminationfrequency may be in one of the UV, visual, and IR spectral bands. Boththe laser source and radiation detector may utilize narrow pass filtersto allow for stealth in illuminating the projectile and simplifiedsignal processing and detector construction. To add stealth, a dyecoating can be applied to the retro-reflective surface to use awell-known “stokes shift” to shift the return signal's frequency from ahigh energy state UV to a lower energy state NIR. Thus it may bepossible to illuminate the projectile with UV laser light whiledetecting the re-emitted light in the NIR spectrum. One should note thatthis feature does reduce the reflected light as the “stokes effect”consumes energy when light shifts from a higher energy wavelength to alower energy wavelength and this approach is not currently supportableusing off the shelf retro-reflective supplies.

Detectors:

An automated system's radiation detector can be included in a spottingscope allowing a sniper's spotter to manually calculate the azimuth andelevation of the next shot. Preferably the radiation detector is anoptical detector or digital camera that measures the ballistic path ofthe projectile at pre-set intervals.

Laser Emission and Reflection for Tracking:

The aim-correcting system preferably includes the following components:

-   -   (1) An emission source of short (strobe) radiation directed to        illuminate the ballistic path of the projectile. It may be        desirable to pulse emissions at predetermined times (T1, T2, T3        . . . ) following firing of the projectile (at time T0).    -   (2) A projectile in flight affixed with retro-reflectors on the        rear of the projectile body.

It is possible to use the two steps above for a visual observation ofthe illuminated shot by a spotter in a sniper-spotter team. It is alsouseful to provide automated tracking and use that feature to provide forimproved ballistic aiming solutions using regressive analysis usingprior shot data.

Automated Tracking:

It is desirable to further automate the system. One approach to automatetracking is a system with the following additional elements (3 to 6):

-   -   (3) A radiation detector for receiving strobe radiation at times        (T1, T2, T3 . . . ) where retro-reflectors reflect the light        along the angle of incidence, returning the light to the        vicinity of the weapon or spotter scope.    -   (4) A signal processor, coupled to the radiation detector, for        processing the electronic signals produced by the detector to        determine the lateral (X) and vertical (Y) coordinates of the        projectile during flight at such times (T1, T2, T3 . . . ) where        retro-reflectors are affixed to the projectile and where the        retro-reflectors reflect light at time T1, T2, T3 . . . ). It        may be useful to utilize a beam-splitting technique for optical        detection.    -   (5) A computer, coupled to the processor, for calculating a        lateral correction and a vertical correction in the aim of the        weapon.    -   (6) An output device, coupled to a ballistic calculator or        computer, to calculate an aiming adjustment of the weapon to        re-aim the next shot placement.

As an alternative automated system to the system described above it ispossible to use an automated system comprising the following elements (7to 9):

-   -   (7) A steerable laser beam that searches an area controlled by a        fast CPU and software algorithm, causing the laser to illuminate        a corner cube or cat's eye on the projectile.    -   (8) A CPU and algorithm, coupled to an imaging device, which        fixes the azimuth and elevation of the return reflection        tracking and further adjusts the azimuth and elevation of the        laser to maintain a track on the illuminated corner cube or        cat's eye.    -   (9) An electronic sensor on the laser beam which detects or        otherwise measures the lateral and horizontal position and        movement changes from the time the projectile's position (X        and Y) is acquired through the projectile's ballistic flight.

Using the actual measurements, an automated device utilizes a regressiveballistic algorithm, coupled with a computer to calculate an improvedaim point for subsequent shots of ammunition. Additional shooting allowsfor repeated regressive analysis to improve the aim-point.

The output device of the system may provide an automated adjusted aimingpoint to the operator or a spotter. Alternatively, the output device mayallow for the manual computation of an adjusted aim point by the spotteror gunner.

In another preferred embodiment of the present invention an otherwiseconventional ammunition projectile is provided with a coating offluorescent dye material, on or near its rear surface, whereby the dyere-emits radiation in response to excitation by laser light.

The fluorescent dye, optimized to luminance in response to laserradiation, exploits a natural phenomenon known as“laser-induced-fluorescence.” The dye is coated on an external rearsurface of the projectile. The coating is preferably covered by atransparent shield or coating and, for example, it may be disposed onthe inside surface of a transparent window on the rear of theprojectile.

The present invention thus provides a system for correcting the aim of aweapon that is operative to launch such a fluorescent dye enhancedprojectile on a ballistic path toward a target. The aim-correctingsystem preferably includes the following components:

-   -   (1) A source of short (strobe) radiation pulses directed toward        the ballistic path of the projectile for excitation of the        fluorescent dye material on the projectile, such pulses being        emitted at predetermined times (T1, T2, T3 . . . ) following        firing of the projectile (at time T0).    -   (2) A radiation detector for receiving strobe radiation        re-emitted by the fluorescent dye on the projectile allowing for        the vertical and lateral measurement of the projectile's        position at times (T1z, T2z, T3z . . . ), where “z” is the time        delay of re-emission after excitation.    -   (3) A signal processor, coupled to the radiation detector, for        processing the electronic signals produced by the detector to        determine the lateral (X) and vertical (Y) coordinates of the        projectile at such times (T1z, T2z, T3z . . . ) during flight.    -   (4) A computer, coupled to the processor, for calculating a        lateral correction and a vertical correction in the aim of the        weapon.    -   (5) An output device, coupled to the computer, for facilitating        an adjustment in the aim of the weapon toward the target, prior        to firing the next projectile.

Using this aim-correcting device the aim of the weapon may be adjustedafter the launch of one projectile to compensate for aiming errors priorto the next launch of another projectile.

By means of this system, either the signal processor or the computercalculates the lateral drift and the vertical drop of the projectile atthe predetermined times.

Preferably the radiation source is laser source adapted to be affixed tothe weapon so that the cone of illumination of the laser sourceintersects with the ballistic path of the projectile and excites thephoto-luminescent material.

Preferably the radiation detector is a digital camera for producing animage of the ballistic path of the projectile.

Depending upon the type of fluorescent dye material, the frequency ofthe excitation radiation may be in one of the UV, visual and IR spectralbands.

Both the laser source and radiation detector may utilize narrow passfilters that provide for stealth in illuminating the projectile andsimplified signal processing and optical detector construction as thetechnique provides for optimized signal to noise ratios.

The radiation source preferably includes a narrow band-pass filter forselectively passing a narrow spectrum of laser light to the projectileto excite the fluorescent dye. The radiation detecting device preferablyalso includes a narrow band pass filter allowing only the re-emittedlight from the fluorescent dye to pass to the detector, therebyminimizing the data processing required of the detector output.

The output device of the system may be a display for the operator whomanually adjusts the aim in the weapon's bore sight or it mayautomatically adjust the aim of the weapon, for example by passing theprojectile drift and drop data to the fire control device of the weapon.

For a full understanding of the present invention, reference should nowbe made to the following detailed description of the preferredembodiments of the invention as illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B and 1C illustrate a Monte Carlo simulation of the impactlocation (against a vertical target) of shots for traced and untraced.308 projectiles fired at a range of 1500 meters. The figures show howthe impact points for a number of tracer shots differ from the impactpoints for projectiles with standard pyrotechnic tracers.

FIGS. 2A and 2B depict an ammunition projectile with retro-reflectorsaffixed at the rear and the sides of the projectile body. that reflectsincident light rearward.

FIG. 2C is a detailed illustration of retro-reflectors, as applied to aprojectile, that reflect incident light rearward.

FIG. 2D illustrates how retro-reflectors are affixed to compensate forthe conning motion in projectiles in ballistic flight.

FIG. 3 is a diagram showing a weapon and the trajectory of a projectilefired from a weapon.

FIG. 4 is a diagram showing a cone of illumination of strobe lightemitted by a laser source that intersects the ballistic flight path of aprojectile fired from a weapon. The laser aim is slightly depressed fromthe bore sight for optimized intersection with the projectile'strajectory within the dispersion of the light cone.

FIG. 5 is a diagram showing a radiation (e.g., optical) detector whichreceives a light reflection from a retro-reflector on the projectile.

FIGS. 6A and B are perspective views of a weapon having a laser sourceilluminating the projectiles in flight and a detector for receivingreflected radiation.

FIG. 7 is a representational diagram showing an error imparted by a firecontrol device which uses ballistic tables and metrological sensors tocalculate a predicted hit point (gunner aiming point). Typically, asniper will observe the impact point of a shot and provide an improvedshot placement for a subsequent shot.

FIG. 8 is a representational diagram showing how the system of thepresent invention identifies the X and Y location of the detectedreflected signals against the sky or backdrop.

FIG. 9 is a representational diagram showing how the system of thepresent invention (the view from fire control device at gunner'sposition) using reflected laser light to allow for registration of theprior shot. The image shows how the an accelerometer or other sensorsmeasures post shot movement of the optical detector such that post shotmovement is measured and the actual X and Y coordinates of an observedshot are corrected.

FIG. 10 is a representational diagram showing how the system of thepresent invention is used, post firing, to shift fields of view. Thesystem measures the angular changes of the platform or camera at thesame moment that the tracer's strobe signal is detected.

FIG. 11 is a representational diagram showing how the fire controlcomputer calculates a new aiming solution after measuring actual driftand drop of an observed “strobe tracer” projectile.

FIGS. 12 and 13 are block diagrams of two systems, respectively, thatuse an algorithm to compute a bore sight adjustment and/or automaticallyadjust the aim point of subsequently fired projectiles.

FIGS. 14A-14E are detailed diagrams of a projectile with aretro-reflective rear surface.

FIG. 15 is a time diagram of laser-induced fluorescence showing thedelay in response to excitation.

FIG. 16 is a representational diagram showing an ammunition projectilehaving a fluorescent dye at its rear surface.

FIG. 17 is a diagram showing an optical detector which receives a lightemission from a laser-illuminated fluorescent dye on an ammunitionprojectile.

FIG. 18 is a block diagram of the system, similar to the systems ofFIGS. 12 and 13, which uses an algorithm to compute a solution for boresight adjustment and/or automatically adjusts the aim point ofsubsequently fired projectiles.

FIGS. 19A and 19B depict the linear beam divergence (in side view andtop view) of 3 m rads and the ballistic trajectory of a .50 caliber(12.7 mm) projectile fired at 500 meters.

FIGS. 19C and 19D depict the transposed linear beam divergence (sideview and top view) of 3 m rads and the ballistic trajectory of a .50caliber (12.7 mm) projectile fired at 2000 meters.

FIG. 20 is a table illustrating the time of flight of a projectile to atarget at ranges from 100-2000 meters. The 3^(rd) column identifies thenumber of projectiles in an automatic volley when a machine gun isfiring at 800 shots per minute rate of fire.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will now be describedwith reference to FIGS. 1-20 of the drawings.

Identical elements in the various figures are designated with the samereference numerals.

First Preferred Embodiment

According to a first preferred embodiment of the present invention, aprojectile is fitted with retro-reflectors on its rear surface. Anemitter is incorporated into a weapon system or into a stand-alone aspotter's scope. The emitter is slightly depressed from the axis of thebarrel and focuses a cone of light in a tight beam that coincides withthe ballistic trajectory of the projectile. The emitter illuminates theprojectile's path in the spectrum allowing a spotter or sensors toprecisely measure the ballistic trajectory. The system may also providethe capability to use automated tracking of the retro-reflectors affixedto a projectile. The invention is a kit that when mounted orincorporated into a weapon or spotting scope provides a methodology toadjust fires.

Cone of Illumination and Retro-Reflectors:

An illuminator emits UV, visual, NIR or MWIR light that illuminates theballistic trajectory of the projectile. When attached to a weapon, theaxis of the cone of illumination is slightly depressed from the centerof axis of the barrel. When using the technique to illuminate an entirecone of light, the dispersion of the light emission and the angle ofdepression illuminate the projectiles ballistic flight path. Theresulting depressed angle and dispersion is calculated for the caliberof the weapon system. Where a MEMs steerable laser beam is used, thelaser search zone is limited to the light cone intersecting theballistic path of the projectile. When incorporated into a sniper'sscope the scope is pointed at the target and the zone of illumination iselevated above the target. The optical radiation traverses the spacebetween the emitter and the projectile and light is reflected fromreflected off the retro-reflectors affixed to the projectile. Theretro-reflectors are affixed to the trajectory to with a geometry toreturn the incidence of light rearward during the trajectory of flightconsidering the yaw of the projectile and angle of attack. The signalmay be continuous or emitted and reflected from the cat's eye or cornercube retro-reflective material affixed to the projectile.

Automated Optical Detection with Pulsed Signals:

Where the signals are pulsed at predetermined times (T1, T2, T3, etc.)following the time of firing (T0), an optical detector incorporated intothe weapon or aligned with the spotting scope detects the angulargeometry (projectile location in the sky) of the radiation reflectedfrom the projectile as well as the duration (time length) of thisreflected strobe in its field of view. The laser strobe emitter emitslight at precise time intervals after launch or cartridge setback. Thecomputer calculates the actual flight position at these precisepost-firing intervals to the location that is forecasted by the originalsolution algorithm. The collected image is digitally processed and X andY coordinates of the projectile's reflected strobe signal are identifiedby the laser's illumination of the projectile at predetermined timeintervals. The “delta” positions are recorded (stored/registered). Whena gunner subsequently wishes to engage new targets, the computerassociated with the system uses an algorithm to identify a precise aimpoint solution using the observed trajectory of previous shots, therebyre-measuring and re-calibrating the distance and relative targetelevation for subsequent firing of the weapon.

Table 1 is a time diagram illustrating the sequence of tracking whenusing strobe illumination signals where a shot where p is the requiredprocessing time for a subsequent fire control solution.

TABLE 1 Sequence of Measurements with Pulsed Signals Sequence ofMeasurement Methodology T0 − a Fire Control Displays solution or aimpoint provided to gunner. T0 − b Measurement of (a) radialAzimuth/Elevation Barrel Centerline and (b) elevation of barrel/firecontrol if not aligned T0 − c Firing Pin Trigger pull (or hammer fallsensor) where a, b and c are lengths of time before T0 T0 Set Back ofCartridge Launch T1 Laser emits short pulse Retro-reflectors on theprojectile reflect light back in the general direction of the origin ofthe shot The illuminated retro-reflectors on the projectile areobserved. T1 + p If an automated system is utilized, the system providesan improved firing solution for the next shot. T2 Laser emits shortpulse Retro-reflectors on the projectile reflect light back in thegeneral direction of the origin of the shot The illuminatedretro-reflectors on the projectile are observed. T2 + p If an automatedsystem is utilized, the system provides an improved firing solution forthe next shot. T3 Laser emits short pulse Retro-reflectors on theprojectile reflect light back in the general direction of the origin ofthe shot The illuminated retro-reflectors on the projectile areobserved. T3 + p If an automated system is utilized, the system providesan improved firing solution for the next shot.

Automated Optical Detection with Continuous Signal Tracing:

New tracking technology includes MEMS steerable lasers that allow forcontinuous X and Y adjustment of a micro laser illuminating a projectileaffixed with a retro-reflector.

FIGS. 1A-1C respectively show a Monte Carlo simulation of sierra balland tracer .308 bullets. Tracer bullets are normally fired in a set mixball to tracer. The mean impact points and dispersion of tracers differsfrom ball projectiles. FIG. 2A shows the dispersion with standard .308cartridge ammunition without tracers. FIG. 2B shows the dispersion of.308 ball tracer cartridges. FIG. 2C shows the dispersion with a mixedball and tracer cartridge combination.

FIG. 2A depicts an ammunition projectile 10 having a retro-reflectivecoating at (42) the base of the projectile or a set of retro-reflectors(43) inset into the projectile body.

FIG. 2B depicts a projectile 10 having a retro-reflective coating (42)and (43) in ballistic flight where the projectile exhibits both conningmotion comprised of pitch and yaw amplitude that vary over the flighttime (44). The retro-reflectors (45) affixed to the projectile arepositioned so that a sufficient surface area of the retro-reflectorshave, during ballistic flight, a rearward angle of incidence to lightemitted from the location of the weapon thereby reflecting light beams(46) to return to the vicinity of the weapon system or spotting scope.The positioning of retro-reflectors accommodates the normal pitch andyaw of a projectile.

FIG. 2C shows a detail of the retro-reflectors.

FIG. 2D is a perspective view depicting an emitter 18, illuminating alight cone 20 that intersects the ballistic path of a projectile inflight 10. The reflected incident light 46 is returned to the opticaldetector 24.

The system of the present invention is shown generally in FIGS. 3, 4 and5. FIG. 3 shows a weapon 12 capable of firing projectiles in thedirection of a target 14. The projectiles impact in the region of thetarget in a dispersion zone 16. FIG. 4 shows a laser source 18 mountedon the barrel of the weapon emitting light in a cone of illumination 20that intersects the projectile 10. FIG. 5 shows light 22 reflected fromthe retro-reflectors 42, 43 on projectile reaching an optical detector24 on or near the weapon 12. This arrangement is illustrated inperspective in FIGS. 6A and 6B.

FIG. 6A illustrates how a narrow beam emitter or laser 18 illuminates aconical area 20 illuminating the projectile 10. The retro-reflectorsaffixed to the projectile 10 reflects light rearward from the projectileto return to the vicinity of the shot. In this perspective the emitter18 and the detector 24 are mounted on the weapon 12.

FIG. 6B illustrates how a MEMS steered laser beam 19 is emitted in alight cone 20 illuminating the projectile 10. The retro-reflectorsaffixed to the projectile 10. Light from the retro-reflectors affixed tothe projectile (not show) reflect light rearward from the projectile toreturn to an optical detector 24. In this perspective the emitter 18 andthe detector 24 are mounted on the weapon 12.

FIG. 7 depicts a solution and actual impact generated by currentgeneration of fire-control devices use ballistic tables and limitedmetrological sensors to calculate a predicted hit point (gunner aimingpoint). Some fire control systems allow users to input manual drift andelevation offsets, but these manual offsets are generally linear.Unsolved contributing errors that diminish the fidelity of fire controlsolutions as many unmeasured errors are omitted from the aimingsolution. The omitted aiming errors devices include (a) bore sightmisalignment, (b) lot-to-lot errors, (c) occasion-to-occasion errors and(d) limitations in existing wind sensor technology. The inability tomeasure unsolved errors degrades the accuracy and precision of weaponfire control solutions, as illustrated in FIG. 7.

FIGS. 8, 9, 10 and 11 depict use of a pulsed technique (from theviewpoint of the gunner or optical detector) where a pulsed light strobesignal is emitted at predetermined times after set back during theflight path of the projectile and reflected back to the location of thegunner or spotter. The fire control device associated with the weaponoptically identifies the x and y position during ballistic flight. Wherea strobe technique is utilized, the measured time is at T1, T2, T3, Tn.Post firing resonance depicted in FIG. 10 can create shifting fields ofview so a system will measures the angular changes of the platform oroptical detector at the same moment that the projectile's strobe signalis recorded.

It should be noted, that the human in the loop remains a formableinfluence as spotters remain critical to the sniper profession.Accordingly, where manual calculations are used the invention providesfor improving the observation and registration of shots as themethodology of reflecting optical emission from a projectile in flightuntil impact enhanced the spotter and sniper's ability to observe andcorrect errors using current practices. The registered informationprovides both an improved manual shooting technique and, whereautomation is available a methodology to track the projectile andimprove the placement of subsequent shots.

FIG. 12 depicts the system for an automated system where the opticaldetector 36 and image processor 38 register the X and Y observationpositions and where a sensor 34 measures the shot and post shotpositions of the optical detector. A clock 48 initiates emitterillumination. The projectiles reflect the emission at T1, T2, T3, Tn andare reflected to the optical detector 36. The computer 40 and software42, calculate the actual registered X and Y position of the ammunitionat specific time. The device is equipped with a fast clock 48 to timestamp shot, images and sensor measurements. Fire control computercalculates a new fire control solution after measuring actual drift anddrop of an observed “strobe tracer” projectile, as illustrated in FIG.10. Sensor 34 may include air temperature, pressure, firing geometry andstandard muzzle velocity. The measurement of observed projectile driftand vertical drop are obtained by an image processor 38 to isolate thestrobe tracer's position. Simultaneously, angular changes in thedetector are measured by sensors 34. The image processor search anddetects the strobe images at pre-set intervals after firing. The opticaldetector 40 can be any type of image capturing device, for example aCCD, video camera, infrared camera or the like. It produces electronicsignals representing the images and passes them to a signal processor42. The processor 42 determines X,Y location and as well as the timeduration of each received response from a projectile in flight. Thisinformation is passed to the computer 40 for calculating a lateralcorrection and a vertical correction in the aim of the weapon 12. Analgorithm 46 written in the software code 42 computes a solution forbore sight adjustment and/or automatically adjusts the aim point ofsubsequently fired projectiles. The adjusted aim point is calculated andrendered in an output 51.

FIG. 13 shows an alternative to the manual measurements or opticalstrobe measurements, wherein the system can use a steerable MEMs laser,where a laser initiates a search pattern within a zone corresponding tothe ballistic flight path and, when illuminating the retro-reflectors,an optical detector.

The system allows the fire control computers to readily observe andcalculate fire control solutions that reduce or eliminate (1)occasion-to-occasion errors, (2) ammunition lot-to-lot errors, and (3)bore sight misalignment.

Fire control computers can readily adjust aim points using sensors tomeasure air temperature, pressure, firing geometry and standard muzzlevelocities; however, practical considerations still limit the accuracyof calculated solutions. Lot-to-Lot ammunition variations along withoccasions-to-occasion errors still result in limitations in the accuracyof fire control solutions. These errors also include those errors thatresult from varying wind conditions. Hence, measurement of the actualobserved projectile drift and drop is necessary to allow fire controlsystems to provide improved aiming solutions.

System Overview:

As illustrated in FIG. 8, the system according to the invention reflectsstrobe laser light emissions at predetermined post firing (post set-backor launch) time windows. The retro-reflectors reflect light pulses thatare collected by the radiation detector 24 (e.g. a camera, spottingscope or optical detector) and are manually or digitally recorded. Ateach pre-set time window the device records changes in the X and Yorientation of the reflected light. The system's image processingsoftware measures the X and Y location of the optical strobe emission atthe pre-set time window.

The system's signal processor identifies the X,Y location of thedetected strobe signal against the sky or backdrop, as shown in FIGS. 9and 10, thereby determining the actual drift and drop of the projectile10 as seen from the gunner's position.

The measurement of observed projectile drift and vertical drop areobtained by an image processor to isolate the strobe tracer's position.Simultaneously, angular changes in the detector are measured. The imageprocessor search and detects the strobe images at pre-set intervalsafter firing.

After detecting the actual observed azimuth drift and drop of acartridge with an emitted light (FIG. 9), a spotter, gunner or theweapon's fire control system can utilize multiple methodologies toprovide improved fire control solutions. The fire control system can (1)reset subsequent fire control solutions to use actual observed drift anddrop, or (2) establish a correction factor which modifies the calculatedfire control solution. Hence, use of actual observed data provides for amore accurate fire control solution.

Fire control computer calculates a new fire control solution aftermeasuring actual drift and drop of an observed “strobe tracer”projectile, as illustrated in FIG. 10.

The diagram of FIG. 11 shows projectile strobe signals from the nextsubsequently fired projectile as viewed from a gunner's position withthe hit point corresponding to aim point.

The system and methodology according to the invention allow fire controldevices to adjust the aim point (in azimuth and elevation) so thatsubsequently fired cartridges hit the intended target by using actualobserved azimuth drift and vertical drop. With the actual drift observedby the fire control's optical sensor, the fire control computercalculates improved solutions for new engagements. As subsequent volleysare fired, the coded regressive algorithm improves the fire controlsolution as it repeatedly measures the actual trajectory of cartridgewith an increasing sample size.

One should also note that the invention can be incorporated intospotting scopes where the observed shot methodology and hand-heldcalculators currently used by snipers is also improved.

In the system shown in FIGS. 12 and 13 an algorithm 46 coded to software42 with a computer 40 refines the aiming solution.

FIGS. 12 and 13 show a system comprising an emitter 33, 61 one or moresensors 34, an optical detector 36, an image or signal processor 38. Thesensors 34 identify various parameters of the weapon 12. A clock, 48time stamps all inputs. Such sensors may include various types includingposition sensors, sensors for gun elevation and the like. In FIG. 12,the emitter 33 is either a focused light source or laser which istriggered by the computer 40 to produce a strobe of light.

In FIG. 13, after a projectile is fired, a sensor initiates a searchtrack for the MEMS laser emitter 61. When the MEMS emitter 61 initiatessearches a pattern illuminating a narrow beam in a cone 20 until itreceives reflected light from the projectile's retro-reflector 10, 42,43.

After acquiring the target, the computer 40 and software 42 directs thesteerable MEMS laser 61. During the projectile's flight, the laser X andY azimuth and elevation corresponds to the steered MEMS laser 61. The Xand Y location of the X and Y MEMS laser azimuth and elevation isrecorded with specific clock time (48) stamps. The computer then runs acoded sub-routine with the regressive algorithm and passes“registration” data output 51 to the fire control device for refinementof the aim point for the next projectile to be fired. Where a return islost, the device reinitiates a search track from the vicinity of theprevious contact in a pattern in the cone 20.

FIGS. 14A-14E show a projectile 60 which may be used with the system inaccordance with this first preferred embodiment of this invention.

FIG. 14A depicts the projectile with a tapered section 61 in the rear.As shown in FIG. 14B the rear surface of the projectile is covered aremovable disc 62 which, when removed prior to firing, reveals aretro-reflector 64.

FIG. 14C shows the projectile in flight with the retro-reflectivesurface 64. As indicted in the enlarged view of FIG. 14D, theretro-reflector is formed in a pattern that generally reflects light inthe direction from whence it came. This pattern, shown in greater detailin FIG. 14E, comprises a grid of star shapes surrounded by diamondshaped patterns of reflective planes. The retro-reflector is held inplace on the projectile 60 by four tabs 66.

Second Preferred Embodiment

According to a second preferred embodiment of the present invention, theprojectile has a layer of photo-luminescent material, instead ofretro-reflective material, on its rear surface. This embodiment of theinvention provides for a method and means collecting optical locationsignals emitted by the luminescent material on the projectile while inflight after firing from a weapon, and for simultaneously recordingmovement and/or acceleration. These optical signals are transmitted froma projectile in either the visual, ultraviolet and infra-red spectrum.The signals are re-emitted from the projectile at predetermined times(T1z, T2z, T3z, etc.) following the time of firing (T0). An opticaldetector incorporated into the weapon launcher or on an associatedplatform detects the angular geometry (projectile location in the sky)of the radiation re-emitted by the photo-luminescent material on theprojectile as well as the duration (time length) of this re-emittedstrobe in its field of view.

FIG. 15 is a time diagram illustrating the time delay of fluorescence inresponse to excitation by laser light. As may be seen, there is a delayof about 3 milliseconds between excitation and response. This period ofdelay is designated hereinafter by the letter “z”.

The operating sequence of the system according to the invention isdepicted in Table 1 below.

TABLE 2 Sequence of Measurements Sequence of Measurement Methodology T0− a Fire Control Displays solution based on solution derived fromalgorithm (based on previous measurement) T0 − b Measurement of (a)radial Azimuth/Elevation Barrel Centerline and (b) elevation ofbarrel/fire control if not aligned T0 − c Firing Pin Trigger pull (orhammer fall sensor) where a, b and c are lengths of time before T0 T0Set Back of Cartridge Launch T1 Laser emits short pulse T1 + z Responseof dye on projectile time z later T1 + z Camera image (x1, y1) of stroberesponse and camera position (xx1, yy1) T2 Laser emits short pulse T2 +z Response of dye on projectile time z later T2 + z Camera image (x2,y2) of strobe response and camera position (xx2, yy2) T3 Laser emitsshort pulse T3 + z Response of dye on projectile time z later T3 + zCamera image (x3, y3) of strobe response and camera position (xx3, yy3)Tn + z Camera image (xn, yn) of strobe response and camera etc. position(xxn, yyn)

FIG. 16 shows an ammunition projectile 110 having a fluorescent dye 111applied to its rear surface. The fluorescent dye preferably has atransparent or translucent coating to protect against damage or it iscovered by a plastic shield or the like attached to the rear of theprojectile.

The system according to the invention has the capability to detect thelaser-induced fluorescence (“LIF”) of a projectile while in flight. There-emission in response to the LIF occurs the short period of time (z)after transmission of the laser strobe excitation.

When a phosphor is included with the projectile dye, the system canutilize phosphor thermometry. By measuring this re-emitted lightduration (z) the system can use temperature differences observed onprojectiles in flight to further differentiate between and among thelocations of multiple projectiles when the rate of fire is such thatmultiple projectiles are in flight at the same time.

The system of the present invention is shown generally in FIG. 17. FIG.17 shows light 122 re-emitted by the fluorescent dye 111 on theprojectile 110, reaching an optical detector 124 on or near the weapon112.

The laser strobe emits light at precise time intervals after launch orcartridge setback. The weapon fire control system compares the actualflight position at these precise post-firing intervals to the locationthat is forecasted by the original solution algorithm. The “delta”positions are recorded (stored/registered) and the fire control providesa gunner with new “corrected” aim points using the registered shots.

The optical signals emitted by the fluorescent dye material on theprojectile are collected by an optical detector, such as an IR camera,co-located with the weapon. The image is digitally processed and X and Ycoordinates of the projectile's strobe signal are identified bycollection at the predetermined time intervals. When a gunnersubsequently wishes to engage new targets, the computer associated withthe system uses an algorithm to identify a precise aim point solutionusing the observed trajectory of previous shots, thereby re-measuringand re-calibrating the distance and relative target elevation forsubsequent firing of the weapon.

Optical emissions include light in the ultraviolet, infra red and visualwavelengths. The weapon's fire control unit has the capability to emit acone of light (modulated to strobe at a set time) that intersects withthe ballistic path of the projectile. Normally, the laser emission willbe aligned vertically. The laser's horizontal alignment will dropslightly at an inclination so the top edge of the laser lightillumination cone is aligned horizontally with the centerline of thebarrel. This geometry allows the laser light cone to cover the entireballistic drop of the projectile.

The laser emitter adjacent the weapon transmits a short, intense lightstrobe signal at predetermined times after set back during the flightpath of the projectile. This occurs at T1=(time of emission+z), T2=(timeof emission+z), T3=(time of emission+z), Tn=(time of emission+z) where zis the time delay in milliseconds. Using this technique it is possibleto select dye combinations where the laser strobe transmits strobesignals at a given frequency and the dye's optical response differs inits response frequency. This is used by the optimize system to precludedetection by potential adversaries. It is possible, in fact, to harnessthe heat of the projectile to change the spectral response of the dye.

The transmission of electromagnetic (optical) signals differs undercertain atmospheric conditions and frequencies. The delay (z) betweenthe laser's production of a light strobe and the tracer's fluorescedre-emitted response, as well as the length (duration) of the responsesignal, are used by the fire-control detection software to eliminatedetection of stray reflective light that occurs when the laser beamstrobe signal reflects off of objects and to distinguish betweenmultiple projectiles.

Projectile flight geometry provides for reflection of light rearward tothe gunner's position at pre-set intervals though the entire flightpath. The fire control device associated with the weapon opticallyidentifies the position (T1=position x1, y1, T2=position x2, y2,T3=position x3, y3, . . . Tn=position xn, yn) of the projectile at setintervals.

The invention provides for a system to collect optical location signalsfrom a projectile in flight which are excited by an optical light source(visual, ultraviolet and infra-red). The fire control uses observedtime-location and angular observation data to compute an improvedballistic solution.

The system allows the fire control computers to readily observe andcalculate fire control solutions that reduce or eliminate (1)occasion-to-occasion errors, (2) ammunition lot-to-lot errors, and (3)bore sight misalignment.

Fire control computers can readily adjust aim points using sensors tomeasure air temperature, pressure, firing geometry and standard muzzlevelocities; however, practical considerations still limit the accuracyof calculated solutions. Lot-to-Lot ammunition variations along withoccasions-to-occasion errors still result in limitations in the accuracyof fire control solutions. These errors also include those errors thatresult from varying wind conditions. Hence, measurement of the actualobserved projectile drift and drop is necessary to allow fire controlsystems to provide improved aiming solutions.

The current generation of fire-control devices use ballistic tables andmetrological sensors to calculate a predicted hit point (gunner aimingpoint). Some fire control systems allow users to input manual drift andelevation offsets, but these manual offsets are generally linear. Hence,the current generation fire control devices continue to provideinaccurate aim points due to the fact that they only calculate a limitednumber of inputs while many “unsolved” sources of errors are notfactored in. Unsolved errors include (a) bore sight misalignment, (b)lot-to-lot errors, (c) occasion-to-occasion errors and (d) limitationsin existing wind sensor technology. All unsolved errors degrade theaccuracy and precision of weapon fire control solutions.

The projectile's stimulated dye response occurs at discrete intervals(at T1+z, T2+z, T3+z, . . . Tn+z, where z is the response delay) thatare observed by fire control devices equipped with optical sensors. Thedye's strobe response to laser illumination identifies the position ofthe projectile at set time intervals after set-back (time T0). Thesystem according to the invention optically collects the strobe lightemissions at predetermined post firing (post set-back or launch) timewindows. The projectile's fluorescent dye emits light strobe pulses thatare collected by an optical detector (e.g. a camera) and digitallyrecorded. At each pre-set time window the device also records changes inthe X and Y orientation of dye emission. The system's image processingsoftware measures or signal processing algorithms calculate the X and Ylocation of the optical strobe emission at the pre-set time window.

The system's signal processor identifies the X,Y location of thedetected dye strobe signal against the sky or backdrop, therebydetermining the actual drift and drop of the projectile as seen from thegunner's position.

The measurement of observed projectile drift and vertical drop areobtained by an image processor to isolate the strobe tracer's position.Simultaneously, angular changes in the detector are measured. The imageprocessor search and detects the strobe images at pre-set intervalsafter firing. Alternatively, the signal processor detects the signal atpre-set intervals after firing.

Post firing resonance can create shifting fields of view. The systemmeasures the angular changes of the platform or optical detector(camera) at the same moment that the projectile's strobe signal isrecorded.

After detecting the actual observed azimuth drift and drop of acartridge, a weapon's fire control system can utilize two methods toprovide improved fire control solutions. The fire control system can (1)reset subsequent fire control solutions to use actual observed drift anddrop, or (2) establish a correction factor which modifies the calculatedfire control solution. Hence, use of actual observed data provides for amore accurate fire control solution.

Fire control computer calculates a new fire control solution aftermeasuring actual drift and drop of an observed “strobe tracer”projectile.

The system and methodology according to the invention allow fire controldevices to adjust the aim point (in azimuth and elevation) so thatsubsequently fired cartridges hit the intended target by using actualobserved azimuth drift and vertical drop. With the actual drift observedby the fire control's optical sensor, the fire control computercalculates improved solutions for new engagements. As subsequent volleysare fired, the fire control may use commonly known mathematicalalgorithms to further improve the precision of the corrected aim pointas it repeatedly measures the actual position of cartridge drift andazimuth with a larger sample size.

In the system shown in FIG. 18 an algorithm computes a solution for boresight adjustment and/or automatically adjusts the aim point ofsubsequently fired projectiles.

The algorithm develops fire control solutions (aim points) using actual,observed azimuth and elevation.

FIG. 18 shows a system 130 according to the invention for a weapon 112comprising an emitter 133, one or more sensors 134, an optical detector(e.g. camera) 136, a signal processor 138 and a computer 140 operatingwith software 142.

The sensors 134 are used to identify various parameters of the weapon112. Such sensors can be of various types, for example, positionsensors, sensors for gun elevation, optical sensors and the like. Theemitter 133 is a high-powered laser which is triggered by the computer140 to produce a strobe of light.

The optical detector 136 can be any type of image capturing device, forexample a video camera, infrared camera or the like. It produceselectronic signals representing the images and passes them to a signalprocessor 138. The processor 138 determines X,Y location and as well asthe time duration of each received response from a projectile in flight.This information is passed to the computer 140 for calculating a lateralcorrection and a vertical correction in the aim of the weapon 112.

The fire control device measures the angular position of the weapon 112when the weapon fires a projectile aimed at a target. This angularposition information includes a radial azimuth/elevation barrelcenterline and elevation of barrel/fire control elevation, The angularposition is measured by the sensors 134 and this information is alsopassed to the computer 140.

The computer determines the drift and drop of the fired projectile andpasses this data to the fire control device for adjusting the aim pointof for the next projectile to be fired.

The time delay (z) of the re-emitted signal allows the computer 140 todisregard reflections received by the detector 138 from stray objects.The time duration of the re-emitted signal allows the computer todistinguish between multiple projectiles in flight which have beenrapidly fired successively by the weapon 112. Closer (and thereforehotter) projectiles will have shorter duration re-emissions that theprojectiles that are further away (and therefore cooler).

Comparison of Systems in First and Second Embodiments:

The first embodiment of the present invention concerns a optically“trackable” projectile fitted with a retro-reflective tracer. Such asystem may be coupled to an apparatus allowing for the recording of theprojectile's flight path and may be coupled with a methodology forimproving the fidelity of aiming solutions in weapons using projectileswith one or more retro-reflectors. In the second preferred embodimentthe projectile uses a projectiles with photo-luminescent material (e.g.,a fluorescent dye) applied to the projectile body to providelaser-induced fluorescence. Like a projectile fitted with aretro-reflector, the projectile may be coupled with a apparatus thatallows for the recording of the projectile's flight path.

In the discussion above, when referring to times T1+z, T2+z, TN+z, z wasthe time addition (in milliseconds) from re-emission delay, postillumination of the laser induced fluorescence. When applying the samemethodology to retro-reflective tracers it is possible to use the sameformulas, but in such a case it is useful to use a definition of “z”whereby z is the time it takes for light to travel (2× back and forth)over the distance after emission. For example, the light from an emitter(with a target at 500 meters) will travel back and forth (1000 meters)in 3.33 micro-seconds. In this circumstance, the technique allows forobtaining distinct range data of the projectiles (in flight) which canbe useful for regressive algorithms. This is also useful fordistinguishing among the many projectiles in flight with a machine gunfiring continuously at 800 rounds per second.

FIGS. 19A and 19B illustrate linear beam divergence (in side view andtop view) for a .50 caliber projectile fired at a target at 500 meters.FIGS. 19C and 19D illustrate linear beam divergence for a .50 caliberprojectile aimed at a target 2000 meters away. As may be seen, thesystem employed in FIGS. 19C and 19D has a steerable MEMS laser emitterthat follows the path of the projectile in flight.

FIG. 20 is a table illustrating the time of flight of a projectile to atarget at ranges from 100-2000 meters. The third column identifies thenumber of projectiles in a automatic volley when a machine gun is firingat an 800 shots per minute rate of fire.

There has thus been shown and described a novel trackable ammunitionprojectile which fulfills all the objects and advantages soughttherefor. Many changes, modifications, variations and other uses andapplications of the subject invention will, however, become apparent tothose skilled in the art after considering this specification and theaccompanying drawings which disclose the preferred embodiments thereof.All such changes, modifications, variations and other uses andapplications which do not depart from the spirit and scope of theinvention are deemed to be covered by the invention, which is to belimited only by the claims which follow.

What is claimed is:
 1. An ammunition projectile configured to be firedfrom a weapon, said projectile having an elongate circular body withside and rear surfaces and a photo-luminescent material, disposed on therear surface, that re-emits radiation at when excited by receipt ofradiation from a radiation source.
 2. The ammunition projectile definedin claim 1, wherein said photo-luminescent material is additionallydisposed on a side surface of the projectile body.
 3. The ammunitionprojectile defined in claim 1, wherein said photo-luminescent materialis a fluorescent dye.
 4. The ammunition projectile defined in claim 3,wherein said fluorescent dye responds to excitation in one of the UV,visual and IR spectral bands.
 5. The ammunition projectile defined inclaim 3, wherein said fluorescent dye responds preferentially to thelaser light illumination in a narrow frequency range.
 6. The ammunitionprojectile defined in claim 3, wherein the fluorescent dye forms acoating on the projectile body.
 7. The ammunition projectile defined inclaim 3, wherein said projectile includes a transparent materialdisposed on the projectile body covering said fluorescent dye.
 8. Theammunition projectile defined in claim 7, wherein said fluorescent dyeforms a coating on an inside surface of said transparent material.
 9. Anammunition projectile configured to be fired from a weapon, saidprojectile having an elongate circular body with side and rear surfacesa retro-reflective element, disposed on the rear surface, thatpreferentially reflects radiation received from a radiation source inthe direction of the radiation source.
 10. The ammunition projectiledefined in claim 9, wherein said retro-reflective element isadditionally disposed on a side surface of the projectile body.
 11. Theammunition projectile defined in claim 9, wherein said retro-reflectiveelement is affixed to the projectile body.
 12. The ammunition projectiledefined in claim 9, wherein said retro-reflective element is coated onthe projectile body.
 13. The ammunition projectile defined in claim 9,wherein said projectile includes a transparent material disposed on theprojectile body covering said retro-reflective element.
 14. Theammunition projectile defined in claim 13, wherein said retro-reflectivematerial forms a coating on an inside surface of said transparentmaterial.
 15. The ammunition projectile defined in claim 9, wherein saidprojectile further includes a protective material that covers theretro-reflective element to protect the retro-reflective element whileexposed to propellant gases.
 16. The ammunition projectile defined inclaim 15, wherein the removable protective shield is a combustiblematerial.
 17. The ammunition projectile defined in claim 9, wherein saidretro-reflective element is positioned and oriented on the projectilebody to allow for the rearward travel of reflected light,notwithstanding a yawing motion of the projectile during flight.
 18. Theammunition projectile defined in claim 9, wherein said retro-reflectiveelement is selected from the group consisting of corner cube reflectors,cat eyes and phase conjugated mirrors.
 19. The ammunition projectiledefined in claim 9, wherein said retro-reflective material is a metalform fitted to, embedded or formed into the projectile's rear housing.